Multi-clad Optical Fiber

ABSTRACT

A multi-clad optical fiber design is described in order to provide low optical loss, a high numerical aperture (NA), and high optical gain for the fundamental propagating mode, the linearly polarized (LP) 01 mode in the UV and visible portion of the optical spectrum. The optical fiber design may contain dopants in order to simultaneously increase the optical gain in the core region while avoiding additional losses during the fiber fabrication process. The optical fiber design may incorporate rare-earth dopants for efficient lasing. Additionally, the modal characteristics of the propagating modes in the optical core promote highly efficient nonlinear mixing, providing for a high beam quality (M2&lt;1.5) output of the emitted light.

This application claims under 35 U.S.C. § 119(e)(1) the benefit of thefiling date of U.S. provisional application Ser. No. 62/488,440 filedApr. 21, 2017, the entire disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the present invention relates generally to opticalfibers, and more particularly, to multi-clad, high power optical fiberswith a high numerical aperture for incoming light, and a high beamquality factor for the output light that operate in the visible regime.

Discussion of Background Arts

Optical fibers have the potential to transform low beam quality (e.g.,M²>>1.5) input light to high beam quality (e.g., M²<1.5) output light,among other functions. However, it is believed that this potential hasessentially only been realized in the IR (infrared) spectrum of light;and then only in the 900 nm to 2000 nm range.

It is believed that prior approaches for multi-clad optical fibers forthe transformation of low beam quality, laser diode light into high beamquality light have several failings, including among other things, afailure to provide or suggest light output in the visible regime.

It is believed that prior approaches for converting low beam qualitylight to high beam quality light in multi-clad optical fibers haveseveral failings, among other things, they fail to address the use ofnon-solarizing fiber materials for efficient nonlinear conversion ofvisible, and for example blue, light.

Thus, it is believed that prior to the present inventions fiberconfiguration having, among other features, a multi-clad structure forhigh power operation, laser diode pumping of the optical fiber, andmode-conversion processes utilizing rare-earth doped ions or stimulatedRaman scattering, and the other features and properties of the presentinventions have never been achieved.

Due to the long interaction lengths of optical fibers, low propagationloss is desired for high efficiency. Low propagation loss is criticalwhen using the third order nonlinear tensor elements, specifically theRaman tensor elements, in optical glass. Chemically and mechanicallystable glass compositions have been disclosed which claim low opticalloss and wider transparency windows than pure fused silica. However, itis believed that all chemically and mechanically stable glasscompositions reported to date have higher optical loss than pure fusedsilica in the visible and UV portion of the optical spectrum. Thus, itis believed that these prior compositions have failed to meet the longstanding need for low propagation loss, and in particular, for silicaalternatives having lower propagation losses than silica for visible andUV light.

In order to make an optical fiber which guides light in the core viatotal internal reflection, the index of refraction of the core must begreater than that of the surrounding cladding region. In the visible andUV portion of the spectrum, the use of aluminum in a silica core havinga silica clad is known, however this approach has several failings,among other failings, it is believed that this approach has the adverseeffect of increasing propagation losses in the visible and UV portion ofthe spectrum.

Another method to further reduce optical loss in fused silica opticalfibers is to introduce excess hydrogen atoms into the pure fused silicaglass matrix to lower losses in the visible and UV portions of theoptical spectrum. This approach has several failings, among otherfailings, it is believed that this approach cannot improve the opticalpropagation losses of blue light when the fused silica glass is dopedwith other materials, such as aluminum or phosphorous.

As used herein, unless expressly stated otherwise, “UV”, “ultra violet”,“UV spectrum”, and “UV portion of the spectrum” and similar terms,should be given their broadest meaning, and would include light in thewavelengths of from about 10 nm to about 400 nm, and from 10 nm to 400nm.

As used herein, unless expressly stated otherwise, the terms “visible”,“visible spectrum”, and “visible portion of the spectrum” and similarterms, should be given their broadest meaning, and would include lightin the wavelengths of from about 380 nm to about 750 nm, and 400 nm to700 nm.

As used herein, unless expressly stated otherwise, the terms “blue laserbeams”, “blue lasers” and “blue” should be given their broadest meaning,and in general refer to systems that provide laser beams, laser beams,laser sources, e.g., lasers and diodes lasers, that provide, e.g.,propagate, a laser beam, or light having a wavelength from about 400 nmto about 500 nm.

As used herein, unless expressly stated otherwise, the terms “greenlaser beams”, “green lasers” and “green” should be given their broadestmeaning, and in general refer to systems that provide laser beams, laserbeams, laser sources, e.g., lasers and diodes lasers, that provide,e.g., propagate, a laser beam, or light having a wavelength from about500 nm to about 575 nm.

Generally, the term “about” as used herein, unless specified otherwise,is meant to encompass a variance or range of ±10%, the experimental orinstrument error associated with obtaining the stated value, andpreferably the larger of these.

This Background of the Invention section is intended to introducevarious aspects of the art, which may be associated with embodiments ofthe present inventions. Thus, the forgoing discussion in this sectionprovides a framework for better understanding the present inventions,and is not to be viewed as an admission of prior art.

SUMMARY

Thus, there has been a long standing and unfulfilled need for low loss,high power, multi-clad, high beam quality optical fibers for visiblelight; including and in particular, for blue, blue-green and greenwavelengths. The present inventions, among other things, solve theseneeds by providing the articles of manufacture, devices and processestaught, and disclosed herein.

Thus, there is provided a multi-clad, fused silica-based optical fiberwhich operates at high power in the visible, and specifically blue,portion of the optical spectrum for converting low brightness, highpower light from blue laser diodes to high power, high brightness bluelight from the output of the optical fiber.

There is provide a fiber and methods of using the fiber to convert alaser beam in one, or more, or all of the visible, UV, and bluewavelengths, to higher beam quality and lower propagation losses, thefused silica based, multi-clad optical fiber having: a core surroundedby a first cladding layer, whereby the optical fiber has a high NA;whereby the fiber is configured to convert low beam quality visible orUV light, having an M²>>1.5, to high beam quality light, having anM²<1.5; a hydrogen dopant, whereby the fiber is configured to providelow propagation losses in the visible or UV portions of the opticalspectrum; and, the core having a GRIN structure.

Additionally, there is provided these fibers and methods having one ormore of the following features: wherein the GRIN structure hascomponents selected from the group consisting of modifiers to the silicaglass to alter the refractive index, structures comprised of the silicaglass to alter the effective refractive index, and modifiers to thesilica glass to shield the core from UV radiation; wherein the firstcladding is surround by a second and the second cladding is surround byan outer cladding, wherein each of the claddings has fused silicaglass.; wherein the first cladding is surround by a second and thesecond cladding is surround by an outer cladding, wherein each of thecladdings has fused silica glass with chemical modifiers; wherein thelow beam quality light is converted to the high beam quality lightthrough direct lasing of rare-earth ions; wherein the low beam qualitylight is converted to the high beam quality light through energyexchange processes induced by nonlinear optics; wherein the opticalpropagation losses are low in both the visible and UV portion of thespectrum; wherein the GRIN structure has components selected from thegroup consisting of phosphorous, aluminum, and aluminum and phosphorous;wherein the GRIN structure has components selected from the groupconsisting of a material that increases the refractive index of purefused silica and does not solarize when irradiated by blue light;configured to exhibits the highest nonlinear gain to the fundamentalmode of the fiber, the LP01 mode; having a second cladding layersurrounding the first cladding layer, wherein the second cladding layerhas an effective refractive index which is lower than the first claddinglayer refractive index; wherein the second cladding layer has modifiersto the glass matrix thereby lowering the refractive index of the secondcladding layer to less than the index of refraction for the firstcladding layer; wherein the second cladding layer has a non-solidstructure thereby lowering the refractive index of the second claddinglayer to less than the index of refraction for the first cladding layer;wherein the second cladding layer has a low index polymer therebylowering the refractive index of the second cladding layer to less thanthe index of refraction for the first cladding layer; having a thirdcladding layer and second cladding layer, wherein the effective index ofthe third cladding layer is higher than the effective index of thesecond cladding layer; having a third cladding layer, wherein theeffective index of the third cladding layer is higher than the effectiveindex of the second cladding layer; comprising a third cladding layer,wherein the effective index of the third cladding layer is lower thanthe effective index of the second cladding layer; and, wherein one ormore of the first cladding layer, the second cladding layer, and thethird cladding layer has a chemical modifier to protect the firstcladdings and core from UV irradiation.

Further there is provide a fiber and methods of using the fiber toconvert a laser beam in one, or more, or all of the visible, UV, andblue wavelengths, to higher beam quality and lower propagation losses,the fused silica based, multi-clad optical fiber which contains thefollowing: one or more cladding layers to produce a high NA; the abilityto convert low beam quality light (M²>>1.5) to high beam quality light(M²<1.5); low propagation losses in the visible and UV portions of theoptical spectrum through hydrogen doping; a graded index (GRIN)structure in the optical core; modifiers to the silica glass to alterthe refractive index; structures comprised of the silica glass to alterthe effective refractive index; modifiers to the silica glass to shieldthe core from UV radiation.

Additionally, there is provided these fibers and methods having one ormore of the following features: which contains an optical core, an innercladding, and 2^(nd) inner cladding, and an outer cladding, all based onfused silica glass or fused silica glass with chemical modifiers; whichconverts low beam quality light (M²>>1.5) to high beam quality light(M²<1.5) through direct lasing of rare-earth ions; which converts lowbeam quality light (M²>>1.5) to high beam quality light (M²<1.5) throughenergy exchange processes induced by nonlinear optics; which containslow optical propagation losses in the UV and visible portion of thespectrum due to hydrogen doping of the silica-based glass; whichcontains a graded index (GRIN) structure in the optical core by theadditional of modifiers to the glass matrix; which contains a gradedindex (GRIN) structure in the optical core by the addition ofphosphorous, aluminum, or some combination of aluminum and phosphorous;wherein the modifier is any element or molecule which increases therefractive index of pure fused silica and does not solarize whenirradiated by blue light; which exhibits the highest nonlinear gain tothe fundamental mode of the fiber, the LP01 mode; which contains a2^(nd) cladding layer with an effective refractive index which is lowerthan the inner cladding refractive index; which uses chemical modifiersto the glass matrix to lower the refractive index of the 2^(nd) claddinglayer; which uses a non-solid structure to lower the refractive index ofthe 2^(nd) cladding layer; which uses a low index polymer to lower therefractive index of the second cladding layer; which contains a 3^(rd)cladding layer with an effective index higher than the 2^(nd) claddinglayer; and, which contains chemical modifiers to protect the innercladdings and core of the optical fiber from UV irradiation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of an embodiment of an index profile for an opticalfiber in accordance with the present inventions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present inventions relate to optical fibers havinglow propagation losses, multi-clad fibers, and configurations of opticalfibers for high power and high brightness light.

An embodiment of the present invention is a multi-clad optical fiber.The multi-clad optical fiber contains several advancements in order toproduce high power, high brightness light from high power, lowbrightness light in the visible portion of the optical spectrum. Thus,this embodiment contains multiple cladding layers, e.g., 2, 3, 4, 5 ormore, in order to accept incoming light confined to high NA (e.g.,0.2>NA>0.8) and convert it to light exiting the fiber in a low NA (e.g.,0.02<NA<0.1). The core is made of pure fused silica combined with agraded-index structure made of phosphorous and/or aluminum and thecladding layers can be made from, for example, pure fused silica,fluorine-doped fused silica, fluorine-germanium-doped pure fused silica,or a photonic crystal structure made from pure fused silica.

The following table lists the relative indices of refraction for oneembodiment of the optical fiber.

Region in fiber Relative refractive index* GRIN core 2.5 × 10⁻³ > Δn > 0(parabolic) Inner cladding 0 Middle cladding −2.5 × 10⁻² Outer cladding0 Polymer jacket  2.5 × 10⁻³ *relative to fused silica at operatingwavelength

In an embodiment the multi-clad configuration the core material is afused silica-based matrix combined with a graded-index structure made ofphosphorous and/or aluminum that is modified through hydrogen doping ofthe glass, which decreases the propagation losses in the visible and UVportions of the optical spectrum.

In an embodiment to provide small effective areas for the conversion oflow brightness light to high brightness light, the center, or innerportion, of the optical fiber is a graded index (“GRIN”) structure. TheGRIN structure is fabricated by the addition of dopants to the innercladding structure, thus only the innermost cladding layer can be dopedfor a circularly symmetric fiber. The dopant can be any non-solarizing,chemically and mechanically stable material element which does notdramatically increases the optical loss, preferably phosphorous, oraluminum, or both. In this manner the GRIN structure forms the opticalcore of the fiber.

The high NA to accept incoming light is produced by additional dopants,and/or a silica-based structure, to lower the effective refractive indexin a region surrounding the inner cladding region. The light may also beconfined by a low index coating such as a low index polymer on theoutside of the fiber.

The following table lists the dopant concentrations and sizes of thepreferred embodiment of the disclosed optical fiber.

Dopant/Concentration Region radius* Region in fiber (mol %) (μm) GRINcore P₂O₅/2.5% @ center 20 H₂/** Inner cladding H₂/** 11.25 Middlecladding F/12.7% 6.25 H₂/** Outer cladding *** 25 H₂/** Polymer coatingN/A 60 *region begins at end of previous region and ends and beginningof next region **H₂/O₂ flame with H₂ surplus, preform temperature ~1000°C., 6.2 days duration *** V (gas flow or gas flows via bubblers):V—GeCL₄/V—SiCl₄: 0.359 V—SF₆/V—SiCl₄: 0.072 V—O₂sur/V—SiCl₄: 6.12

The following table lists the dopant concentration ranges and sizeranges of additional embodiments of the disclosed optical fiber.

Dopant/Concentration Region radius* Region in fiber (mol %) (μm) GRINP₂O₅/0.05-30% 5 ≤ r ≤ 40 Al/0.05-30% H₂/** Inner cladding H₂/** 5 ≤ r ≤50 Middle cladding F/0.05-25% 5 ≤ r ≤ 25 B/0.05-25% H₂/** Outer cladding*** 15 ≤ r ≤ 100 H₂/** Polymer coating N/A 10 ≤ r ≤ 100 *region beginsat end of previous region and ends and beginning of next region **H₂/O₂flame with H₂ surplus, preform temperature ~1000° C., 1-20 days duration*** V (gas flow or gas flows via bubblers): V—GeCL₄/V—SiCl₄: 0.2-0.5V—SF₆/V—SiCl₄: 0.01-0.3 V—O₂sur/V—SiCl₄: 0.5-15

The solarization of the dopants in the GRIN optical core is prevented byadding additional dopants to the outer cladding layer. The preferreddopant is germanium, which can be combined with fluorine for less indexof refraction perturbation in the outer cladding layer. These additionaldopants shield the dopants in the core from UV radiation from theenvironment as well as during the fiber fabrication process.

Multi-clad fibers provide a means of converting high power, lowbrightness light to high power, high brightness light via direct lasingtransition of rare-earth ions or frequency shifting via nonlinearoptics. The small mode effective areas (e.g., 200 μm² or less) and longinteractions lengths (e.g., 50 meters or less) enables high brightnesslight to be created efficiently. Attention has been primarily focused onthe near infrared portions of the spectrum, where the propagation ofoptical fibers, semiconductor pump lasers are readily available, andrare-earth ions have the appropriate absorption and emission bands.Additionally, low propagation losses can result in efficient nonlinearoptical processes, even with the modest nonlinearities offered bysilica-based glasses.

An embodiment of the present invention allows the use of optical fibersin the visible and UV portions of the spectrum to produce high powerwhen converting low brightness light into high brightness light. Thereare, however, few rare-earth ions with substantial absorption andemission cross-sections, in tandem with long upper state lifetimes, inthe visible and UV portions of the spectrum, thus, generally teachingaway from efficient operation using nonlinear optics remains.Advantageously, most nonlinearities increase a function of 1/λ, where λis the wavelength of the light, according to Miller's Rule. Therefore,nonlinear coefficients are higher in the visible and UV portions of thespectrum compared to the near infrared portion of the spectrum. However,losses due to Rayleigh scattering increase as 1/λ⁴, such that theoptical losses soon prevent efficient nonlinear optics from occurring.Additionally, the tail edge of the electronic absorption band edge ofmany materials extends from the UV to the visible portion of thespectrum.

An embodiment of the invention includes the combination of decreasingoptical losses in the UV and visible portions of the spectrum, inconjunction with a multi-clad fiber design to increase the effectivenonlinearity of the optical fiber. The result is an efficient means toconvert low brightness light into high brightness light in the visibleportion of the spectrum in an optical fiber.

Optical fibers for the transmission of and conversion of low beamquality light (M²>>1.5) to high beam quality light (M²<1.5). The lowquality laser beams that are converted by the present systems, and inparticular low quality blue, green and blue green laser beams can haveM² from about 1.55 to about 10, from about 2 to about 5, from about 1.6to about 15, and greater values as well as all values within theseranges. The high quality laser beams that are provided by the conversionof these low quality laser beams, including the low quality blue laserbeams can have M² from about 1.5 to about 1.1, less than 1.5, less than1.4, less than 1.3, theoretically 1, and all values within these ranges.Additionally, the M² values of the converted laser beams provided byembodiments of the present systems can have improved M² values of atleast about 20%, at least about 30%, at least about 40%, at least about50%, and from about 5% to about 50% over the M2 values of the startingor low quality laser beams.

Embodiments of the present optical fibers, in particular for blue,blue-green and green wavelengths, that have NA of from about 0.1 to 0.8,from about 0.2 to about 0.8, equal to or greater than about 0.22, equalto or greater than 0.25, about 0.22, about 0.3, about 0.4 to about 0.5,about 0.5 to about 0.8 and greater and smaller NAs, as well as allvalues within these ranges. High NA as used herein are NAs within thisrange that are greater than 0.22.

Embodiments of the optical fibers provide low propagation losses, inparticular for blue, blue-green and green wavelengths, that are fromabout 10 dB/km to about 40 dB/km, about 10 dB/km to about 30 dB/km,about 20 dB/km to about 40 dB/km, greater than about 15 dB/km, greaterthan about 10 dB/km, and greater and smaller values, as well as allvalues within these ranges.

Turning to FIG. 1 there is a chart showing an embodiment of the relativerefractive index profile from the center of the core to the outer radiusof an embodiment of an optical fiber. In this embodiment, the refractiveindex profile exhibits radial symmetry of the disclosed optical fiber.The dashed line represents the refractive index of pure fused silica forthe intended wavelength or operation. Values higher than the dashed linerepresent refractive indices which are higher than the refractive indexof pure fused silica at the intended wavelength of operation. Valueslower than the dashed line represent refractive indices which are lowerthan the refractive index of pure fused silica at the intendedwavelength of operation.

In this embodiment, the fiber has a core radius of 20 μm, a 1st cladthickness of 11.25 μm, a 2^(nd) clad thickness of 6.25 μm and a 3^(rd)(and outer) clad thickness of 25 μm and an outer coating made up ofpolyimide or acrylate and having a thickness of 60 μm . The baselinerefractive index of pure fused silica is shown by the dotted line 1 atthe wavelength of operation. Starting from the center of the core of theoptical fiber, the GRIN region 2 is shown with an increased refractiveindex with respect to inner cladding region 3. The 2^(nd) claddingregion 4 has a depressed refractive index compared to the inner claddingregion 3 to create a large numerical aperture. An outer cladding region5 is the final glass portion of the optical fiber with a refractiveindex slightly higher than pure fused silica due to the addition of UVabsorbing modifiers near the outer edge of the 2^(nd) cladding region 4.

The GRIN core 2 of the optical fiber contains modifiers which have ahigher refractive index than pure fused silica to create a positiveindex difference between the GRIN core 2 and inner cladding 3. Thepositive refractive index acts as a constant lens inside of the fiber,which forces the effective areas of the lower order modes to be smaller.The smaller effective areas lead to greater energy exchange during theirradiance-dependent nonlinear optical processes, such as four wavemixing, stimulated Brillouin scatter, and stimulated Raman scattering.The modifier is selected such that it does not cause additional losseswhen irradiated by visible light, which precludes elements such asgermanium. This restriction allows the use of aluminum and/orphosphorous in a preferred embodiment.

The modifier is also selected such that the nonlinear coefficient to beutilized in the energy exchange process be increased with respect to theinner cladding layer, viz. the electronic contribution to the X⁽³⁾tensor for four wave mixing, the vibronic contribution to the X⁽³⁾tensor for stimulated Raman scattering, and electrostrictioncontribution to the X⁽³⁾ tensor for stimulated Brillouin scattering. Ina preferred embodiment, the modifier is chosen to be phosphorous due toits efficient coupling and increasing of the Raman gain curve of purefused silica.

Types and Amounts of Modifiers

The purpose of the inner cladding (3) and the 2^(nd) cladding (4) is toprovide the maximum index of refraction difference. A high refractiveindex difference allows light within a defined cone volume to be coupledto the inner clad of the optical fiber. The NA of the fiber is definedas the sine of the maximum angle of the incident light rays, withrespect to the fiber axis, which will be guided into the optical fiberinner cladding. When coupling light into fiber from air, the NA isdefined as NA=(n_(cl,inner) ²−n_(cl,outer) ²)⁰⁵, where n_(cl,inner) isthe index of refraction of the inner cladding (3) and n_(cl,outer) isthe index of refraction of the 2^(nd) cladding (4).

Obtaining a high NA necessitates the use of a lower refractive index forthe 2^(nd) cladding (4) with respect to the inner clad region (3). Inorder to minimize optical losses, a preferred embodiment for the innerclad region is the use of pure fused silica. Modifiers to the fusedsilica glass can be used in order to lower the refractive index. In apreferred embodiment, the modifiers are fluorine, boron, or acombination of fluorine or boron in the 2^(nd) clad (4).

Another preferred embodiment for the 2^(nd) clad region 4 is the use ofa photonic crystal fiber (PCF) structure. The PCF structure is designedsuch that the effective index of refraction of the 2^(nd) clad is lowerthan the inner clad and can be lower than the index of refractionpossible by the use of modifiers in the silica glass, such as fluorine,boron, or a combination of fluorine and boron.

The following table lists the relevant parameters and sizes of the PCFstructure to be used as the 2^(nd) clad region.

Size PCF structure parameter (μm) Air hole diameter 0.5 ≤ d ≤ 5   Airhole wall thickness 0.1 ≤ t ≤ 0.5

-   -   Yet another preferred embodiment of the second cladding region 4        is the use of a UV-curable low index polymer. The polymer is        chosen with minimum absorption in the blue region, and low        refractive index. An example of the proposed fiber is given in        the following table:

Region radius* Region in fiber Composition (μm) GRIN P₂O₅/0.05-30% 5 ≤ r≤ 35 Al/0.05-30% H₂/** Inner cladding H₂/** 0 ≤ r ≤ 10 Polymer claddingLow index polymer 10 ≤ r ≤ 50  (n ≤ 1.38 @ 450 nm) Outer jacket Acrylate10 ≤ r ≤ 100 *region begins at end of previous region and ends andbeginning of next region **H₂/O₂ flame with H₂ surplus, preformtemperature ~1000° C., 1-20 days duration

The outer clad 5 is not meant to guide any optical light but providestwo functions. First, it protects the visible light from interactingwith a mechanically robust outer coating 6 typically placed on theoutside of the outer clad. The outer coating 6 can be metallic, organic,or inorganic. Second, the outer clad contains modifiers which absorb UVlight from interacting with the inner clads 3,4 and core 2 of theoptical fiber.

Another blue fiber laser embodiment is the configurtion where a lightguiding coating on the fiber consists of a low index polymer used toconfine the pump light inside the fiber core. An example of such apolymer is the low index polymer LUVANTIX PC373. Such materials permitvery high numerical apertures i.e. very steep input cones of light whichare subsequently guided by total internal reflection. These polymershave good resistance to optical damage from high power light. Highnumerical apertures (NA) created with polymer coatings exceed the inputangles created by merely doping the cladding glass to create a totalinternal reflection surface. In preferred embodiments NA fibers createdby the use of polymer coating have a NA greater 0.22. In thisembodiment, the fiber core may contain the previously described GRINstructure and may or may not have an interior cladding i.e. the exteriorcoating may serve as the primary or secondary confinement surface forthe pump light.

For blue fiber lasers another embodiment is the case where the fibercore is asymmetric with the pump guiding section of the fiber as is thecase with a D shaped core or elliptically shaped core. In these casesthe purpose of an asymmetric core is to optimize the extraction of thepump modes.

During the fiber fabrication process, the outer coating (6) is appliedin liquid form and exposure to UV light hardens the liquid into a solid,forming the mechanical protective layer to the glass optical fiber. Theexposure of UV to the modifiers in the core can cause additional lossmechanisms, such as color center defects. Including a modifier, ormodifiers, in the outer clad will absorb the UV light during the fiberfabrication process and prohibit the UV light from interacting with themodifiers in the GRIN core and 2^(nd) clad, if present. In a preferredembodiment, the modifier in the outer clad is germanium.

In an embodiment a multi-clad optical fiber design is described in orderto provide low optical loss, a high numerical aperture (NA), and highoptical gain for the fundamental propagating mode, the linearlypolarized (LP) 01 mode in the UV and visible portion of the opticalspectrum. The optical fiber design may contain dopants in order tosimultaneously increase the optical gain in the core region whileavoiding additional losses during the fiber fabrication process. Theoptical fiber design may incorporate rare-earth dopants for efficientlasing. Additionally, the modal characteristics of the propagating modesin the optical core promote highly efficient nonlinear mixing, providingfor a high beam quality (M²<1.5) output of the emitted light.

The following table provide ranges of fiber lengths, optical power in,optical power out, beam quality in, and beam quality out.

Parameter Units Ranges Input Power Watts  5-2000 Output Power Watts0.1-1500 Beam Quality In (M²) N/A  3-100 Beam Quality Out (M²) N/A 1-2 

The following examples are provided to illustrate various embodiments ofthe present laser systems and operations and in particular a blue lasersystem for welding components, including components in electronicstorage devices. These examples are for illustrative purposes and shouldnot be viewed as, and do not otherwise limit the scope of the presentinventions.

EXAMPLE 1

Composition Region radius* Region in fiber (mol %) (μm) GRIN core SiO₂base 20 P₂O₅/2.5% @ center (parabolic) H₂/** Inner cladding SiO₂ base11.25 H₂/** Middle cladding SiO₂ base 6.25 F/12.7% H₂/** Outer claddingSiO₂ base 25 *** H₂/** Polymer coating N/A 60 *region begins at end ofprevious region and ends and beginning of next region **H₂/O₂ flame withH₂ surplus, preform temperature ~1000° C., 6.2 days duration *** V (gasflow or gas flows via bubblers): V—GeCL₄/V—SiCl₄: 0.359 V—SF₆/V—SiCl₄:0.072 V—O₂sur/V—SiCl₄: 6.12

EXAMPLE 2

Composition Region radius* Region in fiber (mol %) (μm) GRIN core SiO₂base 20 P₂O₅/2.5% @ center (parabolic) H₂/** Inner cladding SiO₂ base11.25 H₂/** Middle cladding SiO₂ base 2.4/0.22 **** H₂/** Outer claddingSiO₂ base 25 *** H₂/** Polymer coating N/A 60 *region begins at end ofprevious region and ends and beginning of next region **H₂/O₂ flame withH₂ surplus, preform temperature ~1000° C., 6.2 days duration *** V (gasflow or gas flows via bubblers): V—GeCL₄/V—SiCl₄: 0.359 V—SF₆/V—SiCl₄:0.072 V—O₂sur/V—SiCl₄: 6.12 **** PCF region with air hole diameter/wallthickness listed

EXAMPLE 3

Composition Region radius* Region in fiber (mol %) (μm) GRIN core SiO₂base 12.5 P₂O₅/2.5% @ center (parabolic) H₂/** Inner cladding SiO₂ base11.25 H₂/** Middle cladding SiO₂ base 2.4/0.22 **** H₂/** Outer claddingSiO₂ base 25 *** H₂/** Polymer coating N/A 60 *region begins at end ofprevious region and ends and beginning of next region **H₂/O₂ flame withH₂ surplus, preform temperature ~1000° C., 6.2 days duration *** V (gasflow or gas flows via bubblers): V—GeCL₄/V—SiCl₄: 0.359 V—SF₆/V—SiCl₄:0.072 V—O₂sur/V—SiCl₄: 6.12 **** PCF region with air hole diameter/wallthickness listed

EXAMPLE 4

Composition Region radius* Region in fiber (mol %) (μm) GRIN core SiO₂base 12.5 P₂O₅/2.5% @ center (parabolic) H₂/** Inner cladding SiO₂ base7.5 H₂/** Middle cladding SiO₂ base 2.4/0.22 **** H₂/** Outer claddingSiO₂ base 25 *** H₂/** Polymer coating N/A 60 *region begins at end ofprevious region and ends and beginning of next region **H₂/O₂ flame withH₂ surplus, preform temperature ~1000° C., 6.2 days duration *** V (gasflow or gas flows via bubblers): V—GeCL₄/VSiCl₄: 0.359 V—SF₆/V—SiCl₄:0.072 V—O₂sur/V—SiCl₄: 6.12 **** PCF region with air hole diameter/wallthickness listed

EXAMPLE 5

Composition Region radius* Region in fiber (mol %) (μm) GRIN core SiO₂base 30 P₂O₅/2.5% @ center (parabolic) H₂/** Inner cladding SiO₂ base 20H₂/** Middle cladding SiO₂ base 6.25 F/12.7% H₂/** Outer cladding SiO₂base 25 *** H₂/** Polymer coating N/A 60 *region begins at end ofprevious region and ends and beginning of next region **H₂/O₂ flame withH₂ surplus, preform temperature ~1000° C., 6.2 days duration *** V (gasflow or gas flows via bubblers): V—GeCL₄/V—SiCl₄: 0.359 V—SF₆/V—SiCl₄:0.072 V—O₂sur/V—SiCl₄: 6.12

EXAMPLE 6

Composition Region radius* Region in fiber (mol %) (μm) GRIN core SiO₂base 30 P₂O₅/2.5% @ center (parabolic) H₂/** Inner cladding SiO₂ base 20H₂/** Middle cladding SiO₂ base 2.4/0.22 **** H₂/** Outer cladding SiO₂base 25 *** H₂/** Polymer coating N/A 60 *region begins at end ofprevious region and ends and beginning of next region **H₂/O₂ flame withH₂ surplus, preform temperature ~1000° C., 6.2 days duration *** V (gasflow or gas flows via bubblers): V—GeCL₄/V—SiCl₄: 0.359 V—SF₆/V—SiCl₄:0.072 V—O₂sur/V—SiCl₄: 6.12 **** PCF region with air hole diameter/wallthickness listed

EXAMPLE 7

Composition Region radius* Region in fiber (mol %) (μm) GRIN core SiO₂base 30 P₂O₅/2.5% @ center (parabolic) H₂/** Inner cladding SiO₂ base 10H₂/** Middle cladding SiO₂ base 2.4/0.22 **** H₂/** Outer cladding SiO₂base 25 *** H₂/** Polymer coating N/A 60 *region begins at end ofprevious region and ends and beginning of next region **H₂/O₂ flame withH₂ surplus, preform temperature ~1000° C., 6.2 days duration *** V (gasflow or gas flows via bubblers): V—GeCL₄/V—SiCl₄: 0.359 V—SF₆/V—SiCl₄:0.072 V—O₂sur/V—SiCl₄: 6.12 **** PCF region with air hole diameter/wallthickness listed

EXAMPLE 7A

Composition Region radius* Region in fiber (mol %) (μm) GRIN core SiO₂base 60 P₂O₅/2.5% @ center (parabolic) H₂/** Low Index Luvantix PC373100 Polymer Coating (light guiding) **H₂/O₂ flame with H₂ surplus,preform temperature ~1000° C., 6.2 days duration

EXAMPLE 8

In one preferred embodiment, the inner cladding has a high numericalaperture such that 0.2<NA<0.8.

EXAMPLE 9

In a preferred embodiment, the rare-earth ion is praseodymium. Inanother preferred embodiment, the rare-earth ion is thulium.

EXAMPLE 10

In a preferred embodiment, the nonlinear optics processes do not requirephase-matching, such as stimulated Raman scattering.

EXAMPLE 11

In another embodiment, the nonlinear optics processes requirephase-matching, such as four wave mixing, stimulated Brillouinscattering, or harmonic generation.

EXAMPLE 12

In a preferred embodiment, the hydrogen doping of the silica-based glassis performed at the preform fabrication level. This is accomplished byintroducing a hydrogen-rich flame to the silica-based during thechemical vapor deposition phase of preform fabrication.

EXAMPLE 13

In a preferred embodiment, the chemical modifiers are fluorine, boron,or some combination of fluorine and boron.

EXAMPLE 14

In a preferred embodiment, the non-solid structure in a photonic crystalstructure.

EXAMPLE 15

In a preferred embodiment, the chemical modifier is germanium.

EXAMPLE 16

In another embodiment, the chemical modifier is any element or moleculewhich absorbs UV light to prevent exposure of the inner claddings andcore of the optical fiber to the UV light.

EXAMPLE 17

In another embodiment, the hydrogen doping of the silica glass isperformed after the fabrication of the optical fiber. This isaccomplished by placing the optical fiber in a hydrogen-rich environmentand applying any combination of heat, pressure, or UV radiation topromote hydrogen migration into the silica-based glass matrix.

It should be understood that the use of headings in this specificationis for the purpose of clarity, and is not limiting in any way. Thus, theprocesses and disclosures described under a heading should be read incontext with the entirely of this specification, including the variousexamples. The use of headings in this specification should not limit thescope of protection afforded the present inventions.

It is noted that there is no requirement to provide or address thetheory underlying the novel and groundbreaking processes, materials,performance or other beneficial features and properties that are thesubject of, or associated with, embodiments of the present inventions.Nevertheless, various theories are provided in this specification tofurther advance the art in this area. The theories put forth in thisspecification, and unless expressly stated otherwise, in no way limit,restrict or narrow the scope of protection to be afforded the claimedinventions. These theories many not be required or practiced to utilizethe present inventions. It is further understood that the presentinventions may lead to new, and heretofore unknown theories to explainthe function-features of embodiments of the methods, articles,materials, devices and system of the present inventions; and such laterdeveloped theories shall not limit the scope of protection afforded thepresent inventions.

The various embodiments of systems, equipment, techniques, methods,activities and operations set forth in this specification may be usedfor various other activities and in other fields in addition to thoseset forth herein. Additionally, these embodiments, for example, may beused with: other equipment or activities that may be developed in thefuture; and with existing equipment or activities which may be modified,in-part, based on the teachings of this specification. Further, thevarious embodiments set forth in this specification may be used witheach other in different and various combinations. Thus, for example, theconfigurations provided in the various embodiments of this specificationmay be used with each other; and the scope of protection afforded thepresent inventions should not be limited to a particular embodiment,configuration or arrangement that is set forth in a particularembodiment, example, or in an embodiment in a particular Figure.

The invention may be embodied in other forms than those specificallydisclosed herein without departing from its spirit or essentialcharacteristics. The described embodiments are to be considered in allrespects only as illustrative and not restrictive.

1-18. (canceled)
 19. A method of converting low beam quality light tohigh beam quality of light, the method comprising: (a) directing a laserbeam having a wavelength in the UV and visible wavelength ranges and anM²>1.5 into a fused silica based, multi-clad optical fiber comprising:(i) a silica glass; (ii) a core surrounded by a first cladding layer,whereby the fused silica based, multi-clad optical fiber has a high NA;(iii) the core comprising a GRIN structure; and, (iv) a hydrogen dopant;(v) whereby the fused silica based, multi-clad optical fiber isconfigured to provide low propagation losses in the visible or UVportions of the optical spectrum (b) converting the laser beam in themulti-clad optical fiber to high beam quality light having an M²<1.5.20. The method of claim 1, wherein the GRIN structure comprisescomponents selected from the group consisting of modifiers to the silicaglass to alter the refractive index, structures comprised of the silicaglass to alter the effective refractive index, and modifiers to thesilica glass to shield the core from UV radiation.
 21. The method ofclaim 1 or 2, wherein the first cladding is surround by a second and thesecond cladding is surround by an outer cladding, wherein each of thecladdings comprises fused silica glass.
 22. The method of claim 1 or 2,wherein the first cladding is surround by a second and the secondcladding is surround by an outer cladding, wherein each of the claddingscomprises fused silica glass with chemical modifiers.
 23. The method ofclaim 1, wherein the low beam quality light is converted to the highbeam quality light through direct lasing of rare-earth ions.
 24. Themethod of claim 1, wherein the low beam quality light is converted tothe high beam quality light through energy exchange processes induced bynonlinear optics.
 25. The method of claim 1, wherein the opticalpropagation losses are low in both the visible and UV portion of thespectrum.
 26. The method of claim 1, wherein the GRIN structurecomprises components selected from the group consisting of phosphorous,aluminum, and aluminum and phosphorous.
 27. The method of claim 1,wherein the GRIN structure comprises components selected from the groupconsisting of a material that increases the refractive index of purefused silica and does not solarize when irradiated by blue light. 28.The method of claim 9, wherein the fiber is configured to exhibit thehighest nonlinear gain to the fundamental mode of the fiber, the LP01mode.
 29. The method of claim 1, comprising a second cladding layersurrounding the first cladding layer, wherein the second cladding layerhas an effective refractive index which is lower than the first claddinglayer refractive index.
 30. The method of claim 11, wherein the secondcladding layer comprises modifiers to the glass matrix thereby loweringthe refractive index of the second cladding layer to less than the indexof refraction for the first cladding layer.
 31. The method of claim 11,wherein the second cladding layer comprises a non-solid structurethereby lowering the refractive index of the second cladding layer toless than the index of refraction for the first cladding layer.
 32. Themethod of claim 11, wherein the second cladding layer comprises a lowindex polymer thereby lowering the refractive index of the secondcladding layer to less than the index of refraction for the firstcladding layer.
 33. The method of claim 1, wherein the optical fiberaccording to claim 1, comprising a third cladding layer and secondcladding layer, wherein the effective index of the third cladding layeris higher than the effective index of the second cladding layer.
 34. Themethod of claim 11, wherein the optical fiber comprising a thirdcladding layer, wherein the effective index of the third cladding layeris higher than an effective index of the second cladding layer.
 35. Themethods of claim 11 or 15, wherein one or more of the first claddinglayer, the second cladding layer, and the third cladding layer comprisesa chemical modifier to protect the first claddings and core from UVirradiation.
 36. The method of claim 11, wherein the optical fibercomprises a third cladding layer, wherein the effective index of thethird cladding layer is lower than an effective index of the secondcladding layer.